The invention relates to a transmission emergency release for an automatic transmission which is mechanically blocked when a parking mode is engaged, and includes a manually operable actuating element for mechanical disabling the parking mode.
Automatic transmissions for motor vehicles having an operating range which is divided into various manually selectable operating modes, which are referred to as drive positions. The drive positions include also the parking mode (parking position) and the neutral position. Drive positions of an automatic transmission are selected by the driver on a control unit, resulting in electro-hydraulic actuators to be engaged in the automatic transmission. When the parking mode is engaged, the automatic transmission is mechanically blocked so that the vehicle cannot be towed in the event of a power failure or a fault in the associated electronic control. In order to release this lock, a mechanical emergency release has to be actuated. The same problem exists also in newer automatic transmissions in which control inputs by the driver are transmitted via a shift-by-wire control element electronically to the automatic transmission.
DE 10 2007 011 614 A1 describes a transmission emergency release which is coupled to the gear selector. This apparatus is also suitable for shift-by-wire systems. The transmission emergency release can be activated by a coupling member which can be formed for example as a lever.
DE 199 40 029 A1 discloses a drive position selecting device with an emergency operation for a parking lock, which includes a Bowden cable that is connected to a lever. To trigger the emergency operation, a tensile force is applied upon the Bowden cable so that the lever is pivoted and the automatic transmission is released.
DE 101 40 164 A1 discloses a transmission emergency release in which unlocking is implemented by the transmission selector lever. A release mechanism is secured by a lock, the release mechanism is liberated after unlocking the lock so that the transmission selector can be pivoted beyond a movement limitation, resulting in a release of the parking mode mechanically via a Bowden cable.
Implementing a transmission emergency release requires solution of a number of problems: The cable pull has to be operated by a force that cannot be manually applied, therefore a force multiplication has to be integrated into the emergency release. In order to prevent uncontrolled rolling of the vehicle when operating the emergency release, the foot brake has to be applied at the same time. Thus, the emergency release has to be positioned within reach of the driver. To limit the length of the cable pull, the emergency release must be positioned in the vicinity of the transmission. As a result, only a few locations exist in the vehicle to accommodate the transmission emergency release. When the transmission is located in the front, the emergency release is suitably accommodated in the driver-side footwell. When the transmission is located in the rear, the emergency release is suitably accommodated in the center console or next to the driver seat or in the rear-window shelf when a two-seater is involved.
Conventional transmission emergency releases require large installation space and can be easily installed only in larger vehicles. When small cars or sports cars are involved, this is not possible due to the requirements of body shell, chassis and ergonomics.